Size no longer is as interesting to me as it used to be. I focus more on levels and the spread, even the way the ECNs move, to get a feel for hidden buyers/sellers. I also think that it's more rare to determine when the specialist is handling an order himself, and that it's enough to just see the pressure from other market participants.

In my opinion, I'd try to focus first on determining when one of those big .25-.50 moves is going ot happen via the charts, then learn to watch the tape when those significant setups appear. Be prepared to spend a few years letting it all sink in.